Internal combustion engines, those in which fuel is burned in a chamber for transferring energy to an output shaft, have been thermally inefficient.
The most common types of internal combustion engines have employed reciprocating pistons movable through a cylinder completing a cycle comprising fuel intake, compression, expansion and exhaust.
Four stroke cycle engines have substantial mechanical losses in valve operating mechanisms while two stroke cycle engines incur power loss in compressing scavenging medium.
Rotary internal combustion engines were predecessors of the reciprocating internal combustion engine. However, the rotary engine was for many years considered inferior to reciprocating engines. Recent advances in rotary engine design have resulted in development of rotary engines having speeds, weight per unit of power output, and durability comparable to that of reciprocating engines.
Designers of both rotary and reciprocating internal combustion engines have encountered two basic problem areas in which no satisfactory solution has been heretofore devised.
A first problem area involves scavenging the exhaust gases from the combustion chamber before a new charge of fuel is admitted. Incomplete scavenging results in dilution of the fuel-air mixture by residual gases causing incomplete combustion. Incomplete combustion results in reduction in thermal efficiency and discharge of carbon monoxide and hydrocarbons into the atmosphere.
Many engine manufacturers, as a result of the inability to obtain complete combustion in engines, have attached emission control systems for mixing air with exhaust gases creating combustion in the exhaust system in an effort to complete combustion before exhaust gases are released to the atmosphere to minimize air pollution.
The second problem area has involved leakage of fuel during compression and leakage of expanding gas after ignition of fuel in a combustion chamber.
Rotary engines heretofore devised have employed rotors which were eccentrically mounted on a central shaft, or which had vanes movably secured to a rotor which was eccentrically mounted in an opening formed in a rotor housing. Eccentric mounting of the rotor resulted in a dynamic imbalance of forces while moving vanes, spring urged outwardly to obtain a seal at low speeds, were damaged as a result of excessive centrifugal force at high speeds which caused excessive stress and frictional wear.